This phrase stems from the film "Anchorman". During the seen where Ron is giving his new co-worker a tour of San Diego, he tells her that the city's name means "A Whale's Vagina" in German. This was such an obsurd suggestion that things to this level of proposterousness are therefore refered to as "Whale's Vagina"

Resident Advisor: There will be 24 hour quiet hours this week.
First Year Student: Ma'am, that's whale's vagina!

An exceptionally huge and loose vagina, usually made so by the repeated pounding of many male visitors. It is sometimes such a severe medical condition that the woman loses usefulness when she is finally no longer able to bring a man to orgasm. This condition is a sore side-effect of being a dirty whore. See also itchy vagina, diseased vagina, smelly vagina, STD collector, dirty vagina, putrid vagina.

Ashley informed all her friends that her one-night-stand Tim had an tiny penis when actually she had a slutty whale's vagina.